As technology developments and demands for mobile devices increase, demands for batteries as an energy source are sharply increasing. Thus, many studies are being conducted on batteries that may satisfy various needs.
Typically, in terms of the shape of a battery, demands for polygonal secondary batteries and pouch type secondary batteries increase which may be applied to products, such as cellular phones, due to a thin thickness. And in terms of a material, demands for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries increase, since they have high energy densities, discharging voltages, and output stability.
FIG. 1 schematically illustrates the general structure of a typical pouch type secondary battery according to the related art, as an exploded perspective view.
Referring to FIG. 1, a pouch type secondary battery 100 is configured to include an electrode assembly 300, electrode tabs 310 and 320 extended from the electrode assembly 300, electrode leads 410 and 420 welded to the electrode tabs 310 and 320, and a battery case 200 storing the electrode assembly 300.
The electrode assembly 300 is an electricity generating element including cathodes and anodes sequentially stacked with a separator in between. The electrode assembly 300 is formed in a stacked or stacked/folded structure. The electrode tabs 310 and 320 are extended from each electrode plate of the electrode assembly 300, and the electrode leads 410 and 420 respectively are electrically connected by for example, welding to the plurality of electrode tabs 310 and 320 extended from each electrode plate, and are partially exposed to the outside of the battery case 200. In addition, an insulating film 430 is attached to a part of the top and bottom surfaces of the electrode leads 410 and 420 to increase sealing with the battery case 200 and simultaneously secure an electrical insulating state.
The case 200 is made of an aluminum laminate sheet, provides a space capable of storing the electrode assembly 300, and generally has a pouch shape. In case of a stacked type electrode assembly 300 as in FIG. 1, the inner upper end of the battery case 200 is spaced apart from the electrode assembly 300 at a predetermined gap so that a plurality of cathode tabs 310 and a plurality of anode tabs 320 may be together combined to the electrode leads 410 and 420.
In addition, since the electrode assembly 300 and the battery case 200 are just fixed by sealing the sealed part of the battery case together with the electrode leads 410 and 420, a fixing force is weak. Thus, there is a problem that the electrode assembly 300 moves in the battery case 200.
Meanwhile, FIG. 2 illustrates a partial expanded view of the inner upper end of a battery case where cathode tabs are combined in a dense form and connected to a cathode lead in the secondary battery of FIG. 1.
Referring to FIG. 2, a plurality of cathode tabs 310 extended and protruded from a cathode collector 301 of the electrode assembly 300 are connected to cathode lead 410 in a form of a fused portion integrally combined by for example, welding. The cathode lead 410 is sealed by the battery case 200, in a state that an opposite end 412 to which the fused portion for the cathode tabs has been connected is exposed.
Since the plurality of cathode tabs 310 are integrally combined to form a fused portion, the inner top end of the battery case 200 is spaced apart from the top surface of the electrode assembly 300 at a certain distance, and the cathode tabs 310 of the fused portion are bent in an approximately V shape.
Thus, the combined portion of the electrode tabs and the electrode lead is also referred to as a V-forming portion. For such a pouch type secondary battery, the electrode assembly easily moves along an interface with the battery case, due to the empty space of the V-forming portion when a battery vibrates or falls.
In particular, lithium salt-containing electrolyte injected into the inside of the battery case serves as a kind of lubricant at the interface of the electrode assembly and the battery case, thereby further accelerating the movement of the electrode assembly. Since this movement of the electrode assembly leads to inner short due to the contact of different electrodes at the V-forming portion, and eventually decreases the safety of a battery, there is a need for a way of being capable of securing safety in manufacturing a pouch type battery.
Regarding this, Japanese Laid-Open Patent Publication No. 2005-183820 provides a secondary battery that is configured to incorporate an electrode assembly including cathodes/separators/and anodes in upper and lower battery cases combined in a state of being insulated from each other. Adhesive layers formed of conductive adhesive and organic solvent included in electrolyte each are formed and thermally treated between an electrode forming the outer surface of the electrode assembly and the inner surface of the upper and lower cases. Thus, the electrode assembly is stably fixed to the inside of the battery case, and the electrode of the electrode assembly and the upper and lower cases are electrically connected to one another.
However, since in the technology above, the adhesive layer is manufactured from and coated with paste and exhibits an adhesive property by thermal treatment, there are drawbacks that a battery manufacturing process is generally complex and other components, such as electrode active materials and electrolyte are deteriorated during the thermal treatment process of the adhesive layer.
Thus, there is a big need for a technology capable of fundamentally solving general safety by preventing the movement of the electrode assembly inside the exterior member of a battery.